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Could an aircraft 'hide' in the aircraft shadow of another aircraft without being detected or noticed?
I just finished reading an interesting post where the author suggests that the missing Malaysian Airlines flight 370 could have 'hidden' under the cover of Singapore Airlines flight 68 to fly to a covert airstrip.
I've read multiple thrillers where submarines have hidden behind the acoustic signal of large cargo vessels to mask their sound over sonar arrays, and this (at least in the book) sounds plausible. I also read another book where a bomber (flying under the identity of a commercial jet) masked a business jet to get it into an area without detection. Naturally, both examples are taken from fiction, but I'm wondering:

Would there be any hints now in retrospective to suggest they were being followed? Their transponder was off of course, but I'm wondering if for instance there might be some radio interference or static from such as large aircraft behind them? Are there every any issues when refueling aircraft do this sort of thing?
What is the resolution of radar? Would one be able to notice the two blips on the screen unless they were literally under or beside each other, or would it still appear as one dot on secondary radar if say they were 200 meters behind and below?

Radar resolution is defined in terms of degrees of arc (or alternatively in steradians/solid angles) and as such, the further away from the radar, the larger volume is being sampled.  At altitude and some distance from the radar you should have a bit of leeway on how loose of a formation you can fly and show up as one contact on the radar display.  I'm not giving credence to the theory presented, but I am saying it is plausible that one aircraft could fly a formation with another and be detected as one airplane by a radar.
If the transponder is off, the aircraft you are following will not see you on TCAS  and if you are behind them you will be visually undetectable by the crew or passengers.  If you fly above them you will be clear of their wake, so I would put behind and above the best position to shadow.  A lateral offset might be safer, but if you stray too much, you might wander into the FOV of the cabin.
I can't see any way the following airplane would cause nav or com interference in the followed airplane.
The biggest threat to being detected in this scenario are being seen by other airplane.  If ATC calls traffic and you see two planes in formation instead, you would probably say something.  In the case of the airplane you refer to however, it was night and if you turn all of your position lights, beacons, strobes, tail lights and if there is no moon out you might escape visual detection by a third party.

Great answer. Surely though, manouvering into position above and behind would cause some minor heart attacks at ATC calling the lead aircraft to let them know of unknown aircraft close by. Not having a transponder doesn't mean it's undetectable.

I believe it is practically undetectable to ATC.

@PaulLeigh In that case ATC would see the primary target converging with the full target but the best ATC can say is possible traffic, altitude unknown. ATC may vector the followed aircraft, complicating the intercept. This would be far easier to do in a non-radar environment over open water than over land.

Fighter aircraft routinely fly close to give a false indication of numbers (I used to do it), but close formation is rarely necessary.
The basic resolution angle formula for a radar is 1.22*wavelength/diameter = angular resolution in radians (circular antenna).
For long range Air Traffic Control, typical wavelength is 0.15m, diameter of aerial is 14m. So at 60nm this gives a distance resolution of about 3/4 of a mile. Real antenna have various physical and electronic devices to improve this, so in practice staying at less than 1/10 of this, say 150m, usually means no detection. 150m is the standard FAA specification for its long range radars. We used to use about 75m since we liked to stay "numbers disguised' till about 30nm range.
The real problem for the pilot of MH370 would be that he has very little overtake available to effect the intercept, or a suitable Air Interception radar, which makes it highly unlikely he could have achieved it, as he had no fighter background.
There used to be a prohibition on HF radio ops during aerial refueling but I believe this was for static electric reasons rather than transmission interference. Flying in close formation (5m or less separation) can cause buffeting effects, but basically a plane 75m away is not going to give any indication it's there.
Formation flying is not easy, especially in an airliner!

for the HF radio bit, it has been adressed here

Could one scenario to use this be flying in formation with a scheduled commercial airline flight with full complicity of the crew (and maybe the PAX too) just to piggy back in a military aircraft deep into foreign airspace undetected? Some sort of covert mission or reconnaissance? Or are there flaws that would prevent this. I can't think of how the PAX aircraft would get away though. They'd have to pretend they had no clue.

Theoretically possible once you get close enough. In fact military aircraft do it all the time, making a group of smaller aircraft look like a single larger one.
But there's a catch, getting close enough in the first place, and without being noticed.
The crew and passengers of the other airliner would notice a T7 flying in close formation, and even if they didn't see it, they would notice the buffeting and certainly the proximity alarm on the other airliner would notify the crew, who'd notify ATC, who'd send in fighter aircraft to see what the heck was going on.
And don't forget that it takes rather serious training to get aircraft to fly that close, and close coordination between the aircraft to retain that formation and not crash into one another. All of which would not be in place in your scenario.

So no, it's just another conspiracy theory dreamed up by people who've seen aircraft with crews trained for it fly in close formation at an airshow and didn't know what is involved, just like the idea that the T7 would have flown at wavetop level to avoid radio contact, or diving and weaving through the mountains just over the ground.

I think this is more possible in theory than in fact.
One radar station has given blind spots, but most nations use a whole array of stations.  So if you were not seen on one sensor you'd probably be seen on another.  Plus shadowing behind another jet would likely put you in a zone of dangerous wake turbulence.
Over the ocean it's easier not to be noticed since ATC radar stations are built on land.
Aside from sensors noticing you dilligence is required by those who monitor the sensors.  Seems like that might have been absent on the Malaysian jet, if it actually diverted course radically and crossed the Malaysian peninsula as is being suggested in the news.


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Does the C series from Bombardier incorporate composite materials into the fuselage and/or wings?
Does the C series from Bombardier incorporate composite materials into the fuselage and/or wings? If so, what material is used, and where is it applied. Because of Airbus's 50% market share in the project there might be different technologies applied.
Any help is greatly appreciated.

The Airbus deal is fairly recent, are you asking if that could influence future design changes?

I am asking if there is a use of composited in any component of the C series.

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Who manufactures the landing gear on the Airbus A350 series aircraft?
Where are they made? I assume that they are made out of titanium. Right?

The landing gears are manufactured by Messier-Dowty, a Safran group company. According to their site,

Safran Landing Systems is responsible for the design, development, qualification testing, manufacture and support of the main landing gear for the A350-900 aircraft.

Also,

Safran Landing Systems also provides wheel and carbon brakes for the A350, as well as the landing gear extension-retraction system, monitoring system, steering system and braking system.

The landing gear design does use large amounts of titanium:

The A350-900 main landing gear ... includes the increased use of advanced materials, in particular high strength titanium, corrosion resistant steels
  and HVOF coatings.

A350 landing gear materials, from A350 XWB family & technologies

And the NLG by Liebherr-Aerospace

HVOF coating - looks like pretty intense stuff.  From here https://www.bodycote.com/services/surface-technology/high-velocity-oxygen-fuel-hvof-coating/  "High Velocity Oxygen Fuel (HVOF) coating
High-Velocity Oxygen Fuel (HVOF) coating is a thermal spray coating process used to improve or restore a component’s surface properties ...
Molten or semi-molten materials are sprayed onto the surface by means of the high temperature, high-velocity gas stream, producing a dense spray coating which can be ground to a very high surface finish."

The billet is made either in Russia or China I think. Especially China since they have the largest press and supplies billets to both Liebherr and Safran.

The A350’s NLG (Nose Landing Gear) is manufactured by Liebherr-Aerospace in Lindenberg, Germany:

The A350 XWB nose landing gear is the largest landing gear ever to have been developed and produced by Liebherr-Aerospace Lindenberg GmbH (Germany), Liebherr’s center of excellence for flight control systems and landing gears.
Beside the nose landing gear Liebherr-Aerospace supplies the slat actuation system and various key elements of the flaps.

(liebherr.com)

Welcome to Av.SE!  Can you provide a link to this information? That's helpful so that somebody who would use the info you provided isn't just working off of "somebody on the internet said that..." but has a source to point to.

I included a quote from the website linked in a comment under the other answer. As Ralph said, please always add a credible source to support your answer (where possible). And @nobody comments are ephemeral, it's better to include all relevant information in answers.

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Why do jet engine fan blades have a twisted shape?
I'm thinking: as the blades rotate, the tip moves faster than the hub. So to make the blades efficient, the blades are usually twisted. The angle of attack of the blades at the tip is lower than at the hub because it is moving at a higher velocity than the hub. The amount of thrust generated is higher near the tips than at the root. Engineers want the thrust to be equivalent on every part of the blade. Is that right?

Source: Rolls-Royce plc. flickr.com.

Yes that's about right, but it does not fit the format of this site to put the answer imside the question. Ask the question, then answer your own question in an answer.

The fan is not to generate thrust. It compresses air. The nozzle generates thrust.

The fan most definitely produces thrust. That's a high bypass turbofan we're looking at.

Related to the shape: https://aviation.stackexchange.com/questions/34798/why-do-some-turbofan-blade-have-forward-swept-tips and tangentially https://aviation.stackexchange.com/a/26947/4108

@user3528438, nozzle can't generate thrust, because pressure always acts perpendicular to the surface and in subsonic engines, the nozzle is mostly convergent, so the surface faces slightly forward.

You aerodynamics engineers crack me up!  I see at least four people commenting on the question and one commenting on the -1 answer who sound like they know enough to provide an actual answer.  Yet the person who actually answered got down voted and told he was wrong.  Why not answer the question?

I don't think it's accurate to say that the desired thrust is the same along the entire blade. For a large turbofan blade like the one in your image, the outer part is designed to act more like a propeller (efficient for the bypass air) while the inner part is designed to act more like a compressor (efficient for the core). You're not incorrect in stating that the twist does help optimize the angle of attack with the speed of the section, but that's more about not breaking the speed of sound at the tip than keeping thrust constant along the blade.
For any specific engine, though, the blades are highly optimized based on an incredible amount of complex CFD and wind-tunnel analysis for which there is no simple or intuitive summary. The design of a turbofan blade is driven by several factors, mainly

aerodynamic efficiency,
structural efficiency,
noise,
temperature,
vibrations, and
bird-strike resistance.

All of these go into the resultant shape, but you're unlikely to find specifics that are non-proprietary to the manufacturer and available for anyone to analyze. The twist specifically is just another parameter in the extensive, complicated optimization.

Peter, I disagree extremerly with the statement that "the outer part is designed to act like a propeller". Do you have a reference for this? I have read many books on gas turbine performance, and never ever have read anythng that suggests this. e.g Mattingly's Elements of Propulsion, or Oates Aerothermodynamics of Gas Turbine and Rocket Propulsion, or Gas Turbine Theory by Saravanamuttoo. Performance modeling of the fan is identical to the LPC or HPC - using a compressor map defining pressure ratios, mass flow, and efficiency. But the rest of your comments are correct. Regards

@Richard: The concept I'm trying to convey is that the most efficient thing for bypass air is to move a lot of it with as small a change in velocity as possible (the goal of a propeller) and the most efficient thing for the core is to have the air compressed as much as possible. The turbofan blades need to do both, so some efficiency is lost; the twist is one way of mitigating these losses. Compare a propfan, where the functions are decoupled and higher efficiency can be achieved.

Peter Schilling this is the answer (bounties for this article)

Why do jet engine fan blades have a twisted shape?

Your question is about fan blade twist, but actually the answer is valid for nearly all rotating blades. If a blade weren't twisted, the angle of attack would be very different from its root to its tip.
Twist equalizes the angle of attack along the length. I say equalize for simplification, the angle may not be designed to be equal, other aspects may requires the blade to include some variation of the angle of attack, e.g. to prevent the blade to oscillate (flutter), still the general goal is a to equalize the angle.
Angle of attack
The angle of attack is the angle between airflow and blade chord.

For the blade to be efficient this angle must be close to the maximum lift angle, which is roughly around 15° for usual airfoils:

However we're talking about the direction air actually comes from, as seen by the blade. When the aircraft is moving straight and level, for the pilot air comes from ahead, but this is not true for the fan blade, due to blade rotation.
Velocity created by rotation (tangential velocity) depends whether the point is close to the center of rotation (smaller velocity), or close to the tip (larger velocity).

For a rotating blade, air direction is the (vector) sum of aircraft translation, which is aircraft airspeed, and blade rotation. The sum has a fixed component, the translation, and a variable component, the tangential velocity at the point under consideration:

Let's imagine we have tweaked the blade angle of attack at location A. What happens at locations B and C if the blade is not twisted?

As we move closer to the blade tip, the tangential speed increases relatively to forward speed, so the sum (purple) gets more vertical. Angle of attack is now too small for locations B, and in C it is even negative, that is the blade pushes air in the wrong direction.
To offset air direction rotation as we get closer to the tip, the blade must be twisted by a value shown in gray in the picture above. Near the root where forward motion is the largest, the chord is close to the direction of travel; near the tip where tangential speed is the largest, the chord is nearly in the plane of rotation of the fan:

Source: The excellent Bjorn’s corner
Effect of twist: Varying incidence

The angle of attack of the blades at the tip is lower than at the hub because it is moving at a higher velocity than the hub

From what was discussed we are able to distinguish the actual angle of attack from the apparent angle, which is generally called pitch or incidence, that is the angle between the engine longitudinal axis and the chord.
On a twisted blade, incidence varies, and is larger at blade tip. However the angle of attack, which actually depends on rotational velocity and cannot be evaluated visually, should be more or less constant.
Fan blade specificity in turbofans
In turbofans, the fan acts on two separate flows: Primary flow, the smaller in mass which is used to produce gas to spin the turbine; and secondary flow, the largest which bypasses the engine core and propels the aircraft.
Accordingly, fan blades in such engines are designed in two sections.  Near the hub, blades are part of the low pressure compressor, their role is to increase pressure. Elsewhere they accelerate air a bit to create thrust, like a propeller.
These two designs must deal with their own constraints and optimizations, this gives a particular shape. Modern fan blades are formed hollow sandwiches titanium/aluminum and composites, and are comparatively lighter and more complex. When rotating they are less stressed, in particular where velocity is higher, than heavier blades, and they can be wider without being subject to deformation. This allows to give them a more optimized shape, including twist, taper, dihedral, sweep, etc. The shape evolution over time is visible in the last picture of this answer.

Is it the same reason why compressors are also twisted? The value of relative velocity is different for a hub, tip, and mean radius.

@Auberron: You're right. For compressor blades (and fan blade inner section), there is also a need to make the axial velocity constant from hub to tip to control flow turbulence and so the exit velocity is constant. The purple vector modulus (length) changes from hub to tip, it must be corrected. Velocity is converted into static pressure by next stator, this is the principle of axial compressors. Therefore stationary vanes are twisted for velocity equalization. The blade shape must match the next vane for smooth flow. This plays also a role in blade twist...

... To become familiar with axial velocity and velocity triangle, you may have a look at this video. Someone may suggest a better one.

(Hot section) turbine blades are twisted (in the chord wise direction) because they are partially utilising reactive aero mechanical design, and impulse aero mechanical design. (The blade is also twisted in the radial direction due to vortex flow. See the last paragraph of the development section here. This is also mentioned in Frank Whittle's book, Gasturbine Aerothermodynamics. Rolls Royce's book, "The Jet engine" says on page 50: "The reason for the twist is to make the gas flow from the combustion system do equal work at all positions along the length of the blade and to ensure that the flow enters the exhaust system with a uniform axial velocity.")
With fan blades, I am not so sure - I think your answer is along the right lines, (though it's better to say even pressure rise than thrust, although ultimately that pressure translates to thrust), but if that was the only factor at play, I think the blade shape would be a smooth arc from the hub to the tip, and that's not the case. Usually in a gas turbine, the outer fan case diameter is relatively straight, but the hub expands as the air flows though the fan, then into the compressor, the air travels through a bend. So, the air is moving in an axial and radial direction. This maybe an added factor that causes fan blades to be twisted. Fan and compressor blades have the difficult job of making the air flow in the direction of increasing pressure. Flow seperation will cause stall, so care needs to be taken to avoid any local flow disturbances. The air can also choke within a compressor, which is why sometimes air is bleed of the rear stages for stability control. To avoid choking in one region, the air needs to be distributed evenly. (This is more an issue in the booster or HPC than the fan however). Reducing fan noise is another requirement.
Note: Bits in () in 1st para added in subsequent edit, to include feedback in comments.

Sorry, my first sentence is misleading, and I think that has caused confusion. The first sentence refers only to blades in the turbine (hot) section, as a contextual remark. The rest of the comment is about blades in the cold section - fan, or booster/IPC or HPC. I agree that some fan blades are swept to avoid sonic issues, that results in lower noise and improved performance, as discussed in the related question you highlight.

Because airflow will meet the leading edges at different velocities ( at the hub is slower and needs more AOA and at the external edge is faster and fine pitch is needed ). To benefit from the all available airflow and not get aerodynamic( for compressor) stalled air the twisting must be added to the blades. So to not have Stall of the blades is the answer.

That  way the blades will have a more surface for the diameter and  double action/  reaction response because  if you redirect the airflow that much. So first must take care of the meeting airflow with various points of the diameter of both sides blade and after that to make sure that reaction force is moving airflow at a desired angle (this is part of the 50 degrees you pointed out) . But the twist is because of the different speed.The fan from the initial post is from the engine that bye a good amount of airflow.

You should read this page, this is about propellers, but this is the same principle than for fans. AoA is constant: "For a propeller to operate efficiently, it is desirable to have the majority of the blade at the same angle of attack relative to the local incident airflow [...] Ideally, the whole blade is operating at the lift coefficient at which the blade airfoil achieves its maximum lift-to-drag ratio. We achieve this uniform angle of attack distribution by twisting the propeller blades properly"

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What are regulations for pyrotechnics on planes?
Being in love with both fireworks and flying this is a question that I wondered about for quite some time.
Especially when watching videos like this (which is from 2009 showing a stunt plane flying stunts during night with sparklers on the wings and some single shots) or this (a glider with essentially the same effects like the stunt plane from 2015) I wonder what safety regulations apply.
Most certainly I am not allowed to duct tape some rockets to my wing and light them off remotely mid flight but I haven't heard about a firework rating or something similar either.
What requirements do I have to accomplish to be allowed to fly with pyrotechnics (mainly fireworks) on my plane? This would include anything additional directly in my PPL, permission by local authorities, special safety measures on the plane, etc.
This question is mainly regarding the european room (namely Germany) but I am also looking forward towards answers about regulations from other regions.

"Most certainly I am not allowed to duct tape some rockets to my wing and light them off remotely mid flight but I haven't heard about a firework rating or something similar either." I'm not so sure you aren't allowed. This may fall under "careless or reckless" but if you can prove you were neither, then all you might need is a sign-off from an FBO or possibly just an A&P saying the installation is safe.

In the US, depending on the type of fireworks you might need an ATF permit. I would assume most countries regulate professional type fireworks, whether on a plane or not

Some Navion aircraft where originally equipped with flares to assist  visibility at remote airstrips while landing. There have been several instances in which the pilots ran afoul with authorities on the ground. It violated public or city ordinances. Incidentally the flares have not been available or produced in over 30 years.

I'll answer for the FAA since thats the jurisdiction I know. Like most things some may consider this careless or reckless operation as per 91.13 which is the FAA's catch-all for odd occurrences that are not worth explicitly regulating.

Sec. 91.13
Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person
  may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.
(b) Aircraft operations
  other than for the purpose of air navigation. No person may operate an
  aircraft, other than for the purpose of air navigation, on any part of
  the surface of an airport used by aircraft for air commerce (including
  areas used by those aircraft for receiving or discharging persons or
  cargo), in a careless or reckless manner so as to endanger the life or
  property of another.

I cant find anything that says "you cant tie fireworks to your plane and set them off" but that is an unlikely thing to bother regulating.
The TSA does not allow fireworks to be carried on aircraft and this AOPA article would make it seem as though they are not allowed to be transported by air at all. I would think this includes mounting them to the aircraft so you may be out as a result of this. Your local FSDO may be able to provide some more info on this and what you may need to do to make this ok.
The other thing to consider is that the FAA may consider this "dropping" so you would need to make sure you conform to 91.15.

Sec. 91.15
Dropping objects.
No pilot in command of a civil aircraft may allow any object to be
  dropped from that aircraft in flight that creates a hazard to persons
  or property. However, this section does not prohibit the dropping of
  any object if reasonable precautions are taken to avoid injury or
  damage to persons or property.

If the fireworks are intended to be used in flight and properly integrated into the aircraft, then rules about transportation may not apply. For example, it's very illegal to transport jet fuel on a passenger aircraft, yet there are tons of the stuff on every flight. Other examples are passenger oxygen generators, crew oxygen tanks, lithium ion aircraft batteries and even pressurized tires.

FAA - FAR 14-1-C-43 Appendix A
Part 43 - Major Alterations, Major Repairs, and Preventive Maintenance

(a)Major alterations -

(1) Airframe major alterations. Alterations of the following parts and
    alterations of the following types, when not listed in the aircraft
    specifications issued by the FAA, are airframe major alterations:
(i) Wings.
(ii) Tail surfaces.
(iii) Fuselage.
...
(xiii) Changes to the wing or to fixed or movable control surfaces
       which affect flutter and vibration characteristics.

I think it would be next to impossible to convince the FAA this was not a "major" alteration of the aircraft "wing" or "fuselage". Cameras routinely mounted outside the aircraft violate this same section except for possibly mounting on a strut but the FAA has chosen to ignore it, at least for the time being.
In my experience the FAA will ignore it until someone complains - such as a frightened citizen saying a terrorist is shooting at people from an airplane. At that point you will probably be violated on a number of charges and see some hefty fines and maybe even prison time.
In addition most airport properties and fire departments have laws prohibiting alcohol, firearms, explosives, carriage of flammable products in unauthorized containers, and incendiary devices - depending on the type of fireworks, it will be considered explosive, incendiary, or both.

I see. However there has to be an exception, I guess if people at an airshow may have pyrotechnics mounted (see the linked videos in the question). Especially for events like Oshkosh I expect similar shows to be flown which would definitely draw the FAA's attention. Or would those have to be custom built planes which were approved from the beginning.

Air shows require a special permit from the FAA and local government agencies including the fire department. The permit requires special safety equipment, insurance, operations, and a host of other limitations and requirments.

Yeah, I guess that makes sense. Thanks for the insight!


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Can any aircraft have ETOPS?
I am wondering if any plane can become ETOPS certified? And, is ETOPS the right acronym?

Theoretically anything can be certified if resources are allocated to meet certification requirements. It may not be practical though:

The plane must have at least two engines (obviously)
It must have the range to fly to an alternate on one engine only
Engine failure should not increase cockpit workload too much. Mostly this means some automation system that can operate with asymmetrical thrust.

(2) rules out small twin-engine planes that only have a few hours of endurance on a full tank, and (3) rules out anything without a glass cockpit and avionics suite.
Also, ETOPS is not just about aircraft design; it deals with aircraft maintenance as well. The manufacturer and operator need to come up with a maintenance program that reduces in-flight failures by monitoring various metrics and taking preventive actions before a component fault happens.
Therefore, on some aircrafts, it may not be worth the effort to obtain ETOPS.

Also, ETOPS is a qualification for commercial passenger aircraft - if it's not commercial or it's not passenger, then it doesn't need ETOPS.

Theoretically, could a single-engine plane satisfy the requirements if it had extremely good glide performance?

I don't know how the regulations are written, but the best gliders have a glide ratio of about 70:1, assuming that can be sustained from 30000 feet to the ground that would give a range in still air of about 400 miles. I suspect reality is much worse as it would be difficult to maintain a good glide ratio through widely changing atmospheric conditions.


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What is the minimum price for a full Glass cockpit for the size of 6 passengers aircraft?
I am working on my final project at school and currently looking for the information about avionics system. We design a concept amphibious aircraft with the info as listed below:

2 pilots in the cockpit
6 passengers
Aircraft Mission: Leisure/ Passenger Transport/ Cargo
Cruise speed: 130 knots
Range: 400 to 600 nm
Service Ceiling: 14,000 ft

The customer wants the aircraft to be certified by both FAA and TC with installed IFR system. From FAA I got all the requirement for IFR and decided to design a glass cockpit with a budget of 20,000 - 25,000 USD. However, when looking at the different company such as Honeywell, Bendix/King, Garmin, etc., the price is too high for a newly installed glass cockpit. Therefore, I just wonder if there is any cheap, certified (FAA), and safe products available and what are your opinions regarding the idea of glass cockpit design for the mentioned aircraft above. I saw several cheap products from DYNON and ASPEN, but not very sure if their products are certified by FAA.
I really appreciate any help or comments from you guys. thank you!

Simply, You cannot simultaneously have certified and cheap stuff.

What will be the surface area of the "monitors" ?

I'm not sure you can design and certify a single, simple aircraft instrument like an old-school variometer or pressure gauge and stay within a 25,000 USD budget. In fact, I'm pretty sure you can't. You probably could pull off the design part (old-school instruments are pretty simple as design and construction go, though the implementation requires precision), but 25,000 USD is probably more in line with what the FAA will bill you to even start looking at the design of your single instrument, rather than what certification will cost. Let alone a whole IFR glass cockpit!

DYNON have recently obtained STCs for some of their systems. I believe they are within the budget.

@MichaelKjörling I believe the OP is talking production costs, not development costs. And the FAA provides its services free of charge. It's the cost of providing the data to the FAA that isn't cheap. Also, FAA resources are limited so often you'll need to involve a DER or DAR who will act for the FAA. They do charge for service.

@Gerry Good point, maybe I should have written "before the FAA will look at your design" to be more generic. My general point still holds, though, in that certification is expensive.

Why even use a glass panel in the design?  Can you use seam gauges?

$25k seems really low. I recently saw a quote to modify a Cessna Caravan to a Garmin digital cockpit suite, that was in the region of $150k.


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What is the difference between company routes and pilot routes?
I was trying to find out what are the different route types(flight management system) and found out there is one company route and one pilot route . Are there more different route types ?.What is the difference between the company route and pilot route

A company route, or coroute, is just an easy way for the pilots to download the flight planned route into the FMC, without having to enter every route segment manually. It saves a bit of time, especially on longer routes, and eliminates the risk of input errors.
I haven't heard the term "pilot route" before, but presumably it just means the lack of a company route - i.e. a route that the pilots have entered manually.
Functionally, once the route has been entered in the FMC, there is no difference between a company route and a route entered manually. The only difference between the two is the way they are entered.


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EVTOL(Electrical vertical takeoff and landing) aircraft holding pattern
There is a specific holding pattern and procedures for fixed winged aircraft.Is there any specific holding pattern for EVTOL ? as they have capability to hold a position and altitude .

Wouldn’t any VTOL aircraft follow the same rules and regulations as helicopters regardless of their power source? My understanding is that helicopters use the same holding patterns as fixed wing aircraft. It’s their traffic patterns, IFR minimums, safe altitude minimums, and distance from persons and property that are different.

Hovering takes a lot more power than flying a racetrack pattern.  Besides, how many EVTOL aircraft are actually sharing the airspace with standard fixed wing and helicopters?

Although, some metropolitan areas have specific IFR charts for helicopters, the DFW Helicopter IFR chart I reviewed via ForeFlight shows no specific routes nor holding patterns. Since this chart is for a terminal area, I would assume all Enroute travel would be governed by the common VFR sectionals and IFR High, Low, and Planning charts.

Last year, EASA was developing the framework for rules for small VTOL aircraft. https://www.airbus.com/newsroom/stories/easa-releases-framework-for-vtol-operation.html   I don’t believe it has been finalized. Nor is it expanded worldwide or through ICAO yet. There probably is no rush on the regulation process considering the small number of VTOL aircraft outside of the rotorcraft or ultralight category that are not military at this time. And, the military plays by its own set of rules.

Helicopters can be put in "racetrack" style holds just like fixed wing aircraft, COPTER approaches even include them. There is no reason to believe if/when VTOL aircraft become more prevalent this will be any different.
Hovering is inefficient and difficult which can be made even more complicated when in IMC making it not ideal for a holding maneuver which is often issued to either kill time or allow a pilot time to pull up a new plate or get set up for a new approach.


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What is the difference between Flight data recorder and performance data recorder
Does Flight Data Recorder consists of performance data or both of them are recorded separately.
Do we also have flexibility when to start recording performance data like
Records the initial conditions at the cruise ,climb/des intersection, or current conditions

Do you have any reference to a "performance data recorder"? Typically I've heard of Flight Data Recorder (FDR), Cockpit Voice Recorder (CVR), and Quick Access Recorder (QAR or QDR). Are you referring to the QAR?

@RonBeyer Yes I think QAR , I searched and found most of them use QAR to store performance data


text:
Flight management System(FMS) related to Performance Managment
What are the recommends criteria and requirements for a Flight Management System (FMS) for transport aircraft related to Performance Database or Performance Management


text:
Who has jurisdiction over NMA (non movement areas) at an airport?
Since non movement areas are not controlled by ATC, does that mean the FAA doesn’t have jurisdiction in them? Are NMAs privately owned property inside of a government owned property (I.e FBOs)? Are there rules guiding aircraft in NMAs?
Example: The FAA says transponders should be turned on before taxiing. Does this include NMAs?

The FAA has “jurisdiction” over any aircraft operating in the US, including in places that aren’t airports at all.
A “movement area” is just the portion of an airport where ATC controls movement. It has no effect on any other regulations, such as transponder use.
Consider that the vast majority of airports don’t even have a movement area because they don’t have a control tower. All the other rules still apply.


text:
Why are Flight Directors turned on so early?
I have noticed that the requirement to turn on the Flight Directors in a commercial aircraft is in one of the very first checklists. Why does this have to be the case when the Flight Directors are really just an indication of where the aircraft needs to fly to?
Why, for instance, is it not in the "Before Take-off" checklist?

Well for one example, you need to program in the flight plan into the FD, might as well do it while sitting at the gate than when running through before take-off items.

Depending on what you mean by "a commercial aircraft", they don't. Some companies might have that in their checklist or SOP, but not all do. The air carrier I fly for does not. We usually do turn on the flight director shortly before takeoff via the TOGA button, but it is not a requirement or part of any checklist.

@RonBeyer You don't program a flight plan into the F/D. Flight plans go into the FMS. The F/D gets path data from the FMS when in LNAV (lateral) or VNAV (vertical) guidance modes. The F/D can also track a single path set via several mode options on the Mode Control Panel (MCP).

@Gerry You are right, I mixed up FD and FMS in my mind.

Well, why not...? :)

The FD displays the proper pitch and bank for an aircraft to achieve desired performance.  Having the FD up and ready in advance of takeoff is important to reduce the risk of it not being ready for use at takeoff.  The FD normally receives input from the primary flight gyros, and uses that input to calculate control commands.  Those control commands can be directly routed to an autopilot, or displayed for pilot to utilize.
Gyros need to be spun-up and ready, and the FD computer needs to be initialized and calculating solutions at takeoff time, so delaying the startup to takeoff could cause delay due to non-readiness.
Additionally, FD and FMS work together, and typically FMS is powered up when the avionics are initially powered up.  This permits routing, and other pre-flight tasks to be performed on the FMS.  Most larger aircraft, and particularly long haul aircraft will have dual FMS, usually independently programmed by different crew members.
In general, powering up avionics tends to reduce corrosion, assure operation, permit self-tests to be performed in advance of leaving the gate, and has little cost compared to operational benefit (such as a return to the ramp for OTS equipment).

This doesn't answer the question which is about the Flight Director, which together with the autopilot and autothrust systems comprise the autoflight systems.  It is totally independent of the navigation systems you're discussing.

@Gerry, you are absolutely correct, and I have modified my answer accordingly. Thank you.


text:
Why is an F22 slower than an F15?
An F22 has a higher thrust to weight ratio. The F22 has around ~70,000lbf thrust from its F119 engines, where as the F15 has around ~48,000lbf thrust from its F100 engines.
But every metric I can find indicates that the top speed of the F15 is higher than the top speed of the F22 (though I have not found a concrete reliable source on either).
How is this the case?

With stealth, the goal is to shoot before the other plane realizes you are there. If you actually get into a dog fight, you've already made several mistakes.

I am aware of this fact and not sure how it at all relates to the question of speed.

related: Why is the maximum speed of current fighter aircraft lower than those from the 1960's and 1970's?

Higher thrust to weight ratio mainly mean better acceleration and climbing rate, not higher top speed.

@ScottF Before stealth, the enemy could see you coming, so you had to get there, strike and get away before they could react. If they can’t see you, though, you can conserve fuel (and extend range or increase payload) by flying slower.

Aerodynamic heating will damage or destroy the composite wing of the F-22, especially around the leading edge where compression heating is highest. See here for the temperatures which supersonic flight causes.
Therefore, the F-22 has been restricted to Mach 1.8 for short duration and Mach 1.6 for prolonged flight. More speed will not be needed, anyway.
The internal weapons storage of the F-22 makes it bulkier than the F-15 which causes more wave drag. Also, the engine intakes were not designed to operate at speeds above Mach 2, so pressure recovery in them drops at higher speed. These two factors will affect the top speed of the F-22 negatively, so I would not be surprised if the F-15 is faster even without restrictions on the F-22 speed.

If I understand correctly, wave drag is the direct answer to the question. The first part (no need to go faster) explains why 70.000 lbf is sufficient

@MSalters: I have no drag polars of both, but argue from first principles. I think that the intakes have even more to do with the lower speed. And temperature is still an issue.

Is the plane hard limited to mach 1.8, or could a pilot override that in certain scenarios?

@ScottF: Hard limiting the top speed of an aircraft is impossible. Even if the engines are automatically cut to idle, a simple dive lets it accelerate again. Therefore, an override is possible.

@Peter Kämpf: But if the hard-limited top speed is already faster than the terminal velocity of the aircraft, then cutting to idle and diving would not cause acceleration, right? From Mach 1.8, wouldn't cutting to idle cause a deceleration of the aircraft, regardless of pitch or orientation?

@AaronHolmes Depends on altitude. In high density air the aircraft will slow down, but near the ceiling it won't in a vertical dive.

The F-15 was specified to have a maximum speed of Mach 2.5.  However, I believe this was reached only once during Developmental Test and Evaluation and they had to change the engines afterwards.  On the production models, there was an overheat switch in order to get to this speed, but the A model only had 11,300 lbs of gas so having this capability was a joke.  And the switch had a wire the pilot had to break to throw it.  All supersonic aircraft with the exception of the SR-71, the F-111 and Soviet MiG-25 did not have enough gas to make top speed usable.  People forget the  three main parts of fighter aircraft performance, thrust to weight ratio, wing loading, but equally important is its fuel fraction.  Most jet fighters have fuel fractions between 25% to 30%, that is, at takeoff gross weight you divide that into how much internal fuel the fighter can carry and you get the fuel fraction.  Why is this important?  Well the fuel fraction tells you how far you can fly or stay in air combat and return.  In the case of the F-111 it had a fuel fraction of 38% so it could stay supersonic for awhile. The surprising thing about the MiG-25 is that its fuel fraction is only 26% while the SR-71 fuel fraction is 56%.  The MiG-31 has a fuel fraction of 47%.  The other part of this is how fast the engine burns fuel measured in Thrust specific fuel consumption, that is,how much fuel does the engine need to produce the required thrust for a given altitude and speed condtion.


text:
How many aircraft and pilots can a part 135 cover?
If you form an LLC for charter flights, can you hire an unlimited number of pilots to fly under the same part 135 certificate (assuming all are commercial pilots), or does each pilot and/or each aircraft (all aircraft owned by the LLC) need to have their own part 135 certificate?

There is no restriction on the number, type of aircraft, or pilots for a "Full 135 Operator."
There are 4 levels of 135 operators:

Single-Pilot Operator
Single Pilot-in-Command
Basic 135 Operator
Full 135 Operator *

Source: http://usac.com/faa/InstructionTwo.asp?Product=Full%20135%20Operator

There are 4 levels of 135 operators:

Single-Pilot Operator
Single Pilot-in-Command
Basic 135 Operator
Full 135 Operator

In #1 and #2, as the name implies, you can only have a single pilot.  As for #3, you can have up to 3 pilots but the requirements on the organization and support staff increase (e.g. you will need a dedicated Director of Maintenance).
Option #4 is fully unrestricted and comes with the greatest amount of responsibility.  You will need a Chief Pilot, training program, manuals, and a host of other requirements.
My advice is if you intend to have multiple pilots, try for #4.  It will give you the most flexibility and in the end, make your 135 easier to sell down the road.  Expect the process to take between 6months and a year to complete.


text:
How does the flyboard air get sufficient lift/thrust with such small form factor?
How does the flyboard air get so much thrust when it can't have more than an 6" disc area (if that) on each of its four lift engines?
Isn't the thrust of a rotor = CT * p * Area * tipSpeed^2?
(CT - coefficient of thrust, p = air density, tip speed = linear speed at tip of rotor).
Shouldn't this limit the thrust such small rotors can create without the tips exceeding mach (and causing all the associated problems with that)?
How much thrust could each of these really be generating? I'm assuming their ducted fans, but still shouldn't be enough, should it?
It's also clearly not ground effect as it reaches heights well above where that would be relevant (claimed height of 1000 feet, though the videos tend to show only up to around 50-75ft).

Source:
http://www.guinnessworldrecords.com/news/2016/4/confirmed-franky-zapata-sets-new-farthest-hoverboard-flight-record-in-france-427011

Flyboard is turbine-powered, based on what I've seen and read.

A ducted fan is not limited by Mach like an open propeller.

Maybe you should rewrite your question, asking for purely technical data, e.g. what is the theoretical maximum thrust that can be generated by a rotor with n blades of size m at p rpm? And let the Guinness stuff alone (as we don't have the full description of the propulsion system).

Right -- I think that's the main misconception.  There are variants of the Flyboard that have been referred to in various news stories, but the present one that I think is being referred does, as egid says, run on kerosene-powered turbine engines, which are relatively common.  Asking for what the powerplants are, maybe the rationale for using turbines vs. ducted fans/open rotors would be good (https://www.theverge.com/2016/4/15/11439798/franky-zapata-racing-jet-powered-flying-hoverboard-interview).


text:
Can an ADS-B In/Out equipped aircraft increase ground station coverage?
Suppose a ground station can detect aircraft in a 200 km radius with ADS-B In.
There is a plane A at 180 km, and another one B at 250 km, both equipped with ADS-B In/Out.
If ground station receives A, and A receives B: Can B information go to ground station using A as a repeater?


text:
Can repeated call-signs be present in one day?
I am working with a big ADS-B traffic sample of one day Europe, and identified repeated call signs. Examples include:

Flight that ends in an airport and repeated call sign starts from there.
Two flights with the same call sign, ADEP and ADES.
Four Different ADEP and ADES.

I thought in one day it was not possible to have repeated call signs.
Is this possible? Is my data wrong?

It is no problem to have the same call sign on the same day. As long as the same call sign is not uses at the same time there is no problem.
For VFR flights, the same call sign can even be used at the same time as long as it is not in the same airspace.
Many of the ADS-B duplicated call signs on a single are aircraft registrations coded in the transponder's aircraft ID field, typically from General Aviation flights

Thank you for your response. A related question: Should call signs be ICAO codes? I detected plane models that appear as call sign: CL60, CL30, B737, B738... and some strange call signs like 1234ABCD.

I have rarely seen such aircraft ID's being transmitted. What is the source of your data? Is it from FR24 or similar?

Yes, historic samples from one of this services.

They modify the call signs based on other information they have; what you see in not what was transmitted. For many aircraft they will withhold the identity of the aircraft and replace the call sign by a generic type identification.

@DanielViaño Those 8-digit codes are internal FR24 identifiers. Read this answer about those

@DanielViaño Also, I've found FR24's system to be really glitchy. One aircraft turns into two quite often. I'm not sure why but I suspect it's due to their system anticipating the path in between ads-b updates. I think it must confuse the system sometimes when an aircraft is in a different position than the computer expects it to be, so it ends up creating a duplicate "ghost" aircraft with the same call sign


text:
Where should I find a Pratt & Whitney Canada PT6 operator's manual?
I'm studying the PT6 in detail but the infos I get around the web are sometimes lacking in depth of informations.
I'm pretty much interested in the power curve vs RPM of this engine.
Where should I be able to find out the operators manual of the PT6?

the manufacturer?

There are multiple variants of the PT-6 are you asking about a specific one? Parameters may also change based on the airframe its installed on.

@ratchetfreak Pratt&Whitney

I meant ask the manuacturer

It probably is not meant to be available in the public domain for free. (Not to say that there aren't any bootleg copies out there.)  If you need it, you may well have to buy it. Start with P&W and see what they can tell you.

Found it here
https://www.manualslib.com/manual/812510/Pratt-And-Whitney-Canada-Pt6a-Turboprop.html?page=1
First hit on google for "Pratt & Whitney Canada PT6 operator's manual"

That's a generic instructions manual. Not the Operator's manual. Thanks tho.


text:
Flying from right seat of Socata TB9 - confused about Pilot manual limitation (US regulations)
I was comfortable flying from the right seat in my Grumman American AA5A and would let non-pilots sit in the left seat to introduce them to flying. I was expecting to do the same in a friend's TB9, but this text gave me pause.
Given the the Socata TB9 (Tampico) is generally considered a primary trainer I was surprised to find the following in section 2 (Limitations) of the Pilot Information Manual

CREW LIMITATIONS Minimum crew: 1 pilot
  (1 pilot required at L.H.
  station)

I am confused how to interpret this.

How is it legal for a CFI to train a "non pilot"?
Does it mean that as long as there is a body in the left seat anyone can fly it (from the right seat?)
What does "pilot" mean in this case in the Pilot Manual? Is "Student pilot" defined only when there is a CFI in the right seat?

I have seen placards on tandem airplanes that allow "solo flight" from one of the two positions for what I expect are CG limitations - but am baffled by the perceived limitation in this manual as-written.

Most airplanes are designed for the pilot to be in the left hand position, so some have controls on the left side that are inaccessible (or very hard to reach) in the right hand position, like parking brakes, fuel tank selectors, nosewheel tillers (on big jets), sometimes the key is hard to reach. On the TB9 the circuit breaker panel is by the LH pilot's leg, it would be extremely challenging for someone in the RH seat to reach those, and they could be important if one blows in flight or there's a fire.
The important things is that the person in the left seat is capable of and has been briefed on how to operate any controls required during the flight.
Personally I don't see why you need to let people sit in the left seat to give them a taste of flying, the right seat is just as good for that and it is less risky.

I can see why you might want to fly most Pipers, Beechcraft, and Mooneys from the right seat since they only have one door. But the TB series all have two doors so it doesn’t make a lot of sense unless you are training for your CFI.

They only have one door but that's not a good reason to sit on the right @JScarry. The left seater has no problem reaching the levers to open the door, and in an emergency scrambling out on your hands and knees from the left seat, while undignified, gets you out as quick as having to get your feet under you on the right.


text:
Difference between Flight path and Route
What is the Difference between a Route and Flight path

Can you give us some context so that we can understand your confusion? Because they are really just synonyms: Route, flight path, track, course, etc. all pretty much mean "where the airplane goes"...

Your route of flight is what you plan, planned, or are planning to fly. Your flight path is what you are actually flying or will be flying based on your current track, heading, speed, and attitude. They can be one in the same.

While I tend to agree (at least in some contexts), I'm not sure those are official definitions. Do you have a source?

I also tend to agree, but they are really interchangeable depending on the tense.  And I think the source is the English dictionary, these aren't unique terms....

I think “flight path” is sometimes used to describe the 3 dimensional path through the air. (includes altitude)


text:
Do navigation databases (by e.g. Aeronavdata or Jeppesen) include company routes?
Does the navigation database provided by database providers like Aeronavdata or Jeppesen etc include company routes?

How are the company routes maintained; are they modifiable by the OEMs?
Is the navigation database customizable?

Any insight on this will be helpful.

Helpful in what way?

By OEM do you mean the FMC manufacturer or the Database vendor?

The company routes are maintained by your company.  Some FMS installations have a computer program where you can create the company routes and upload them to each FMS.  Other FMS requires each FMS to be programmed.
All FMS have the ability to see if the routes have been changed due to a database change.   If the pilots wanted to use those company routes the FMS would require them to verify the routes are stored correctly.


text:
How do interceptors communicate with the airplane crew when the radio is dead?
A week ago an airplane lost the radio connection to the tower due to technical difficulties in German airspace (article in german). Thats why interceptors started to escort the plane and to check if everything was fine or an act of terrorism is happening. But how can they determine if there was a hijacking in progress of everythin is fine if the radio is dead?
Q: How are the interceptors communicating with the airplane?


text:
How to write a good aircraft maintenance work card?
Is there any guidance for writing the aircraft maintenance work cards? I want to find out some articles or books talking about this topic as I just start new job on it. How to write a good aircraft maintenance work card?

Have a look at ATA Spec 100 and ATA Spec 2200. 100 can easily be found on google.

Not specific to aircraft maintenance, but here are some pointers for writing about technical subjects: https://writers.stackexchange.com/questions/9247/what-are-best-practices-when-writing-technical-descriptions/9281#9281


text:
How to measure the aircraft maintenance cost of a operator?
How to measure the aircraft maintenance cost of a operator? What tool or mechanism can be used to measure such performance? Or what index can be used to determine the performance?

You would have to have access to the airline's internal data.

Assume I have the data, I mean how to do the analysis.

Maintenance costs are generally expressed as dollars per flight hour for a particular aircraft type.  Chargeable labour hours, parts, overhauls, delay costs, repairs etc., on airplane model X, divided by that airline's total flight hours on that particular type.
This kind of data will be broken down and tracked at the Line Replaceable Unit level as an hourly operating cost of the LRU itself.  Like, say, a hydraulic pump will have all expenses related to maintaining that particular part number, including repairs, overhauls, and chargeable delays/cancellations caused by failures, all added up to a global dollar amount per flight hour for that pump.  This is also tracked by the aircraft manufacturer for the entire fleet.
That number will be used to assess whether the pump is better or worse than the global fleet for that aircraft type, or compared to the same pump used on other aircraft models, to decide whether to pay for improvements, look into changing the maintenance practices, soft timing the pump (overhauling sooner than the legal requirement), and other actions.  There will be some alarm threshold established, say >$1.00 per hour, or 85 cents/hour or whatever, the airline will use to determine whether something should be done or not.
If the pump manufacturer introduces a product reliability improvement, it will be sold to the airline as providing X cents reduction in hourly costs of that LRU, along with X percent improvement in dispatch reliability. The airline will do a business case to decide if the long term saving is worth the up front expense.  They usually go by a payback period, where for example the projected hourly saving from doing an upgrade will pay for the cost of the upgrade within 5 years, or less depending on how cheap the operator is (over the last 10-15 years, a lot of US regionals have been only buying upgrades that pay for themselves in 1 year).


text:
Why do passenger jet manufacturers design their planes with stall prevention systems?
I understand why passenger jets use software that overrides pilot inputs that might cause the jet to exceed the flight envelope.  But why do passenger jet manufacturers design their planes with stall prevention systems?  Shouldn't professional pilots be well aware that a stall is possible when the airspeed is too low, or the angle of attack is too high?

This isn't as simple as it sounds, and AF447 really set this in motion for the industry. The problem is that at differing altitudes your AoA between "flying" and "stall" can be extremely narrow. Couple that in with no visual references and a pilot may not know that the aircraft is stalling...

Be aware, especially on the more advanced, larger aircraft, although the anti-stall systems do pull and act largely on their own against pilot input, 20lb's of force is roughly the industry standard (I believe from personal experience) to override this.

@RonBeyer AF447 had such a system, but it had been disabled due to erroneous airspeed readings when the pitot tubes iced. If anything, AF447 is something of a cautionary tale of pilots becoming too reliant on such systems instead of knowing how to fly the airplane themselves.

Because stalls are really bad?

I feel "to prevent stalls" might not be the answer you're looking for, but I think it's accurate.

I don't have enough knowledge to write a comprehensive answer, but part of it is thinking the system should keep the aircraft within it's flight envelope. Most of the time this works, but then there are many cases where it doesn't and the result is lots of dead people. I can't imagine pilot recovery being possible with these newer overly automated systems like UA 232 https://en.wikipedia.org/wiki/United_Airlines_Flight_232 .

Why do car manufacturers install seat belts? Shouldn't licensed drivers be well aware that they should slow down when it's raining or snowing and that they shouldn't run through red lights or stop signs?
A better analogy:
Why do car manufacturers install anti-lock break systems? Shouldn't drivers know that when their brakes lock up they should release brake pressure and/or pump the brakes quickly to slow the car down?*
*To be fair, I don't think this is actually taught in driver's education (at least in the US) anymore - my kids learned this from me, but never reported being taught and/or practicing when they took driver's ed. One of the many reasons flying is safer than driving.

Because accidents happen.
Because pilots are human and make mistakes.
Because when you're flying in the clouds with no visual references, it's easy to get confused.
Because even with stall warning & prevention systems in place, confused pilots will fight the system. AF 447

And because even with stall prevention systems, stalls are still a reality. That's how bad it is

To be fair the AF 447's stall prevention were disabled because of incorrect airspeed readings.  In contrast, the Lion Air 737 crash was that it didn't get disabled... die if you do, die if you don't...

I believe some planes have a nose wing set at a steeper angle than the main wing, causing the nose to stall first, thus bringing the nose down before a real stall is reached. (See https://www.ainonline.com/sites/default/files/uploads/2018/07/web0dpp_0434.jpg for an example of a nose wing, though I don't know its purpose on the Piaggo.)

@user3070485 that "nose wing" is called a canard, and yes, I believe you're correct. I would imagine that it's still possible to stall a canard winged aircraft, though that would make a good question of its own.

@FreeMan It is still possible to stall a canard aircraft but most are designed as @ user3070485 mentioned where the canard will stall first.  However this becomes a more difficult situation when you introduce leading and trailing edge devices which alter the stall characteristics of the wing. You can get a situation where the canard will stall first under certain configurations and where the wing will stall first under others.

AF447’s systems were not disabled.   AF447’s envelope protection failed because a needed sensor failed, or to be more precise, 3 redundant sensors all of the same make and model operating in the same conditions. Also contributory: they don't bother fitting actual stall sensors, they just look at airspeed, altitude, flaps, stated weight etc. and compute when stall would be expected.  Losing airspeed and altitude sensors breaks that.

Air France 447 is actually the worst example of a "safety system." It's exactly what the OP is questioning. "The stall warnings stopped, as all airspeed indications were now considered invalid by the aircraft's computer due to the high angle of attack." The stall system gave warnings when the pilots did the correct thing. Shitty software is precisely what killed all those people. I'm pretty sure that is the gist of the OP's question, why allow software to overrule the pilots. There may be cases where the result is beneficial, but there are cases where it is not; like AF 447.

@James I am quite sure that pulling all the way back on the stick at all times is not the pilots doing the right thing on AF447.  Pulling back all the way on the stick is what you do when you are evil and trying to intentionally stall the airplane into the sea.    It's well established that if the pilots had simply let go of the controls, the plane would have righted itself.

@Harper, that point is irrelevant. At the point the pilots were attempting to recover from the stall, by nosing down, the software crossed the AoA threshold into "reasonable inputs" and the stall warnings sounded again, where they were silent before. That created negative reinforcement feedback to the pilots and confused them so much that the plane crashed where it was a totally recoverable situation. That software design flaw cost over 200 people their lives.

@James No.  When the stall warning returned, the idiot again pulled full back on the stick, (without mentioning this to the pilot flying), dooming what chance of recovery might have remained.  Please explain to me how that is anything other than the stupidest, most destructive action possible?  What on earth could the guy possibly have been trying to accomplish?

Spam cans (light single engine planes like 172s) have downward lift on the elevators. And, when angle of attack is high or forward airspeed low, that lift diminishes, tending to pitch the plane down to restore a safer angle of attack. It's stable, but it comes at the cost of wasted lift. The forward-elevator canard arrangement (Rutan designs for example) avoids the wasted lift.

To be certifiable, airplanes have to have some kind of cues to warn when you are getting close to a stall, and have decent behaviour during the stall, because nobody is perfect.  Airplanes with very strong physical cues prior to stall, like the whole airframe shaking, and good behaviour during a stall, like a good natural pitch over tendency with immediate unstalling of the wing, can get away without stall warning and prevention systems.
Transport aircraft with highly loaded wings and high performance airfoils may have poor behaviour before the stall (no buffeting or shaking), and poor recovery performance after, and need a little help.   The airfoils used for airplanes that fly at near trans-sonic speeds tend to suffer from this because they tend to stall from the leading edge, at which point the wing stops lifting all at once, and there is often no prior buffeting or shaking.
The earlier supercritical (higher critical mach#) airfoils developed in the 70s were especially bad for this because they developed a flow separation bubble just aft of the leading edge at high angles of attack, due to the profile that was used to manage the formation of shock waves (the Challenger business jet and CRJ200 Regional Jet is typical).  You do not want to experience the natural stall on such an aircraft and some kind of system has to be in place as a backup for mishandling of the airplane by the pilot.
For airplanes with mechanical/hydraulic controls, to provide a tactile warning as a substitute or supplement for the airplane shaking (pre-stall buffet), stick shakers are used, which is just a motor with an eccentric weight on the control column.  If the post stall behaviour (not much natural pitch over, or worse, settling into an unrecoverable deep stall) is poor, a stick pusher is installed to give the control column a shove just before the natural stall occurs.  The stall protection system calculates when to do all this.
Most high performance aircraft use shakers, and some use stick pushers.  With FBW, the FBW computers intervene directly within the control loop to achieve the same end without having to shake or push the controls.

In the Air France 447 accident, the Airbus A330 only had a sound warning, with no physical warning, and the plane was clearly built so that it can't "get away" without a warning. Why is that?

The last sentence in my post applies.  It's a FBW airplane with side sticks and the computers control the airplane at the margins, only letting the pilot input go so far, with an aural warning when things are getting close, but the computers will simply not allow the pilot to go all the way into an aerodynamic stall.  447 wasn't stalled in the aerodynamic sense on its ride down, it was being held at the maximum attitude the computers would allow, not quite stalled, because the right seater was in a mental fog panic mode holding the right side stick fully aft the entire ride down.

And the guy in the left seat was in a similar mentally saturated state and didn't think to hit the left seater's override button to pitch the plane over.  He pushed his stick forward a few times but this only gets a 50% input because the two inputs are averaged, unless he overrides, and a 50% input wasn't enough to recover from the low speed mush descent.

The cockpit recorded did record the sound of the audible stall warning for the entire decent, so I would agree that the pilots were in a mental fog and completely did not register what they needed to do.

This is one of the biggest problems in the industry.  Pilots go through fast track schools and end up in airliners that are AP engaged 95% of the time and have never really learned how to fly, like the guy who learned on gliders, flew in the bush, flew multi-engine s**boxes hauling crap, for a number or years, to the point where the basic fundamental instincts are burned in.  They know what to do, but it's not sufficiently internalized, so when weird stuff happens and the stress level goes to 11, they freeze in confusion.

You said you understand systems to prevent the airplane from exceeding the flight envelope. Stall is just another boundary of the flight envelope. The rest of the envelope limitations are listed in the flight manual as well. Shouldn't pilots know not to stall the airplane, just as they know not to over-stress it, or exceed other limitations? Of course.
But humans make mistakes, they can get distracted or disoriented. And just as there's little benefit to allowing a pilot to rip the wings off the plane by pitching too fast, there's little benefit from allowing the plane to stall.
Here is a selection of aircraft that have crashed due to stalls.
South Airlines Flight 8971
Air Algérie 5017
AirAsia QZ8501
Thai Airways International flight 261
Vladivostokavia Flight 352
N452DA
Yemenia Airways Flight 626
If stall protection systems are implemented and functioning properly, they can prevent issues. Here are just a few instances where stall protection worked as intended:
GoAir 338
Air France 7662
Jetstar 248

On the flip size, I'm curious what would have happened to Asiana 214 if it had had a stall prevention system. If I'm remembering correctly, they did stall (or at least very nearly stall) on very short final while trying to make the runway. If a stall prevention system had prevented them from raising the nose, would they have hit the nose on the seawall instead of the tail? That seems like it could have been a bad situation a whole lot worse.

@reirab True. On the other hand, if you allow the aircraft to run into two limits simultaneously (out of room and out of speed), there is not much anyone can do. You could argue the „opposite“ safety system, too, and say an automatic terrain escape manoeuvre would be fantastic, except with Asiana 214, it could have worsened the stall...

@CptReynolds Agreed. The root source of the problem was, of course, lack of energy on very short final, which was totally a result of pilot error. But, given that situation, they pretty much had to choose how they were going to crash rather than whether they were going to crash. In that sort of situation, I'd personally prefer a human pilot who can look out the window and make rapid judgments based on the exact situation in control. It's just not the sort of thing that's easy to account for when you're designing a computer program.

I suggest to add  Colgan 3407 to the list.

I think there may also be a slight game of numbers played by some airlines. The chances of an aircraft crashing are very slim, and well-trained pilots are more expensive (at least to train). I think the entire industry is seeing the results of a couple of decades of it simply not being worth pursuing an airline career, so there aren't enough young, experienced pilots. Thus, countries with less strict airmen certification or operation standards end up with less experienced pilots operating well beyond their capabilities.

Flying airplanes is easy. I can teach someone to safely fly an airplane in good conditions in about 10-15 hours of flight time. But actually being a pilot, especially in situations where an aircraft system is malfunctioning and giving incorrect feedback, is very hard and can take many, many more hours to reach that skill level.

@reirab I believe USAir 1549 had the same problem.  I seem to recall Sully admitting that the alpha protection prevented him from flaring it correctly for a ditching, resulting in the tail taking structural damage, seriously injuring a FA and letting water rush in.

The relevant certification requirements, set by the FAA/JAA/CAA etc require that a "large aircraft" that is capable of stalling has an automatic stall warning and recovery system. So the simple answer is "because the rule of law says so".
Maybe you could think about re-phrasing the question to ask why the traditional stick shaker and pusher, with a long and satisfactory history, were not used? I expect that Boeing will be having to answer that question to the authorities.

I agree entirely that your re-phrasing would have improved the question, but it's probably too late now :(

Well, stall is a limit to flight envelope, the one exceeding which is most dangerous, so stall prevention system is one of the systems that override pilot input if it would lead to exceeding the flight envelope.
And note that stall is directly related to pilot input, because in stable aircraft¹ the angle of attack is directly controlled by elevator and stabilizer position² and stall occurs when the critical for given configuration is exceeded.

¹ All transport aircraft are longitudinally stable. Only unstable aircraft are some new fighters (and some very early experiments).
² The stability makes the aircraft always pitch so as to assume the “trimmed” angle of attack determined by the control surface position. It is a first order feedback, so no oscillations, and it takes really abrupt control input, or severe turbulence, to create a significant momentary deviation.


text:
Why is the position of the pilots' head (eyes) so important?
From this question:
What are these Lights on Center Holm between Windows on the A320?
I learn that the pilots' eye position is important. Enough to justify an extra piece of equipment.
But why? Can't a pilot tell if they see enough, above/below/on each side, by just looking?

The correct seating position is important to ensure

A consistent viewpoint, which results in the final approach and flare always looking the same to the pilot. This is important when hand-flying the aircraft to ensure consistent landings.

Having a consistent viewpoint gives several operational advantages such as easing the handling of the aircraft by providing pilots with a consistent visual reference, repeatable at every flight. This is especially useful during final approach to be familiarized with the final approach path angle and also for the flare phase.

Best forward visibility, which maximizes the area in front of the aircraft you can see (Visual Segment):

Having the seat further backwards or lower would reduce the Visual Segment.

Good View of the Instruments, which allows seeing the PFD and ND without having to move your head down. This is how it looks with the correct seating position:

And this is how it looks if you are seated too high or too far forwards:

All sources: Airbus - Are You Properly Seated?

You also asked

Can't a pilot tell if they see enough, above/below/on each side, by just looking?

Yes, not all aircraft have the three balls for finding the optimum seat position. You can do it by looking over the glareshield and ensuring good visibility of the PFD/ND. On Boeing aircraft, this is how it is supposed to be done since they don't have a dedicated eye reference indicator:

Pilot Seat Adjustment
Adjust the seat position with the appropriate controls to obtain the optimum eye
reference position. Use the handhold above the forward window to assist. The
following sight references are used:

Sight along the upper surface of the glareshield with a small amount of
the airplane nose structure visible (A)
Sight over the control column (in the neutral position) until the bottom
edge of the outboard display unit is visible (B).

(Boeing 737 NG FCOMv2 - 1.40.44 Airplane General - System Description)

It's even more critical in aircraft with a HUD. Proper eye position ensures the attitude reference and flight path vector are consistent with the actual aircraft path. And if it's also equipped with enhanced or synthetic vision, it ensures the supplemental vision information overlays the 'real world' image acurately.

It's just a shortcut aid based on the OEM's ergonomics engineering.  The sweet spot is considered to be with your eyes high enough to see down to the base of the windshield without obstructing anything on the instrument panel.
This puts your preferred sight line roughly on the plane of the coaming/glareshield extending toward you from the base of the windshield (or slightly above or below), when the seat is positioned to the typical for/aft position for a comfortable hold on the control wheel (roughly a forearm's length from your torso).
When you get in there are 3 steps:

Set the seat for and aft to suit your forearm length to the control wheel or side stick.
Set the seat height to align the balls, or whatever your personal preference is.
Set the rudder pedal adjustment (called the stature adjustment) to your leg length, making sure you can apply full rudder plus push the brake on that side fully on with your toe while your leg is stretched out.

Not everybody likes the recommended location set by the balls.  When I was flying CRJs, which had the balls on the center post, I would ignore them most of the time and just set the height to put my sight line where I could just see the top surface of the glareshield, which, as it happens, more or less aligns the balls.
The eye height most pilots will set with or without the balls tends to be the same, and the seat setting you find when you get in tends to reflect the torso length of the previous pilot.  I have a long torso and short legs, kind of orangutan-ish, so the next person after me usually would find the seat set pretty close to the floor.

To answer the second part of your question, the short answer is ‘No’.
We use perspective to judge taxiing manoeuvers (turns) and to achieve the correct initial pitch attitude on take-off and on landing.
We need certain visual cues to determine correct positioning over the threshold of the runway. When perspective is used, a reference point is needed by which to gauge your position. That reference point must remain the same the entire time.
An example:
On take-off in poor visibility, we need to see 4 runway lights to confirm whether or not we can depart. An incorrectly adjusted seat could mean a delayed take-off or an illegal one.
Another example:
On landing, at 50ft we need to see the threshold disappear under the nose. This helps to ensure that we are neither too high nor too low (both of which can lead to disaster). Adjusting seat height alters that visual cue with potential serious consequences.

Welcome to [aviation.se]. This appears to be very good info, if you would [edit] it to break it up a bit, it will be much more readable and make it a very good answer.

Airplane designers analyze and test the heck out of the airplane-pilot system. That very hard problem becomes less hard if they remove the flexibility of where can the pilot eyes be.


text:
How much can I exceed crosswind limits by?
I'm learning in a Tomahawk. They have a maximum demonstrated crosswind component of 15 knots. My school has a limit of 12 kt, but will only allow students to fly in 50% of that, so 6 kt.
Since it's very windy where I live, that's not going to allow to get out much over the winter.
So, once I am allowed to solo, what can I realistically push the limit to? I have read of people getting away with close to 20. I just want to get out as much as possible. I understand this might increase the risk slightly of an incident.

Wow, you've come a long way from your "FoF". Scared to get in an aircraft to exceeding crosswind limits in, what, 6 months(ish)?

@Jamiec I still don't like flying in jets. Small aircraft don't bother me... I don't know why. Maybe it's a control thing.

@Jamiec Never mind the fact that two weeks ago, OP was learning to fly an Ikarus-C42, and now they're in a Tomahawk. Those are quite different. And their first ever flight lesson was in the second half of October, if I read another question correctly.

Pfft, C42, Traumahawk, B747 - they're all just two wings and an engine or 4. Same thing, no? :D

"I think there would be something euphoric about going 'that way'." And this is another very strong reason not to become a pilot.  Simply put, you've gone from afraid to suicidal.  Get out of the cockpit.

At least here in the US, each solo must be endorsed and the instructors often add limitations like maximum wind and minimum ceiling/vis for the flight to take place. Getting your solo endorsement isn't a license, each time you go out you still have to be under the supervision of an instructor.

@RonBeyer - more or less the exact same in the UK. There's no way a decent instructor would sign you off for a solo (on their license!) in anything even approaching max crosswind.

"Also, after listening to the ATC of the recent engineer who hijacked and crashed the plane after doing a few somersaults... I think there would be something euphoric about going 'that way'. So I'm not scared anymore"-- well, government agents will be knocking at your door soon.  I'm sure you won't be allowed to rent an aircraft anywhere, ever again.

@Jamiec Seconding this. There should be a full and comprehensive brief before each and every solo flight, and if the crosswinds do become too much while airborne - the answer is to divert. You should have more than sufficient fuel to do so (I don't think I ever launched solo without a full tank during training)

Aviation safety isn't just meant to protect the pilot from death (or permanent disability!), but also people on the ground (either directly, or indirectly through the risk of emergency driving / work). Don't be that guy.

Bad plan man. You shouldn’t be doing this at this point.

What do you think will happen if your instructor checks your logbook and sees that you soloed on a day when the crosswind never got below, say 10 kt (a bit more than half again the student limit, but below the school limit, so you might manage to check the airplane out of the hangar)?  Even if you "get away with it", those limits were put there for your safety, and to protect an airplane you don't own.
In fact, if "what can I get away with" is your general approach to things, you might want to reconsider becoming a pilot.  They truthfully say "There are old pilots, and there are bold pilots, but there aren't many old, bold pilots."

Besides safety (which I completely agree with the other answers) major considerations for keeping to limits are insurance coverage and staying within regulation:

If you willfully exceed limits and have an accident your insurer may not cover the costs as they expect pilots to act responsibly and reasonably. Flying 10 knots over the demonstrated limit gives them an out, some would say rightfully so
Every set of flying regulations I know of gives authorities a way to pull your ticket if you are caught flying irresponsibly. In the US it's FAR 91.13 pertaining to "careless OR reckless" operation of an aircraft, in the UK the CAA has a similar rule although I can't remember the exact wording of it. Although these rules are open to interpretation flying an airplane in conditions the airplane and/or pilot cannot handle would be considered reckless

@757toga OP has given their location previously as being in the UK, so no 91.13 for them. Highly likely other, similar regulations, though.

@757toga Indeed, and as I said, very similar. LAPL vs PPL - Which is more suitable? gives OP's location as "The training will take place in the UK, although I will be moving to France shortly after obtaining either license." on Oct 5.

You can "push the limit" to whatever you feel comfortable with. You can even push it beyond the demonstrated limit if you're inclined to do so. Don't expect many people to rent you their aircraft for very long (assuming it survives) if you continue to do so.
Just yesterday I went out an practiced my crosswind technique by doing a bunch of circuits in a PA28 (pretty similar to the tomahawk you're flying) an a varying 6-15kt wind almost completely across the runway. It was not pleasant, it was not fun. I would not choose to fly often in those conditions - being that I still consider myself pretty inexperienced at ~200hrs. For a very low hours pre-solo pilot to even consider it is, in my opinion, nuts. It's completely the wrong attitude to safety.
However, for what it's worth, we live with the same UK weather and I can tell you there is a load of good flying over the winter months. Most of our wind is prevailing westerly, and most of our airstrips are oriented East/West for exactly that reason. Your limiting factor will be cloud base, not wind, most of the time and no amount of bravado (stupidity!) will let you fly in that under VFR.

Wholeheartedly second the bravado/stupidity dichotomy. One difference between PA-28 and PA-38 is asymmetric stall nastiness. I wouldn’t want to venture close to any low speed asymmetric stuff in a Tomahawk.

There is no way we can tell you by how much you will be able to exceed your school's limits without risking damage to the airframe or other property, or injury to yourself or others.
Maximum demonstrated crosswind component means just that: maximum demonstrated. However, limits are set for a reason.
Yes, a good pilot might well be able to exceed the maximum demonstrated crosswind component and still fly, and land, without damaging anything. (Notice that I very deliberately do not say "safely" here.) Maximum demonstrated crosswind is supposed to be managable by ordinary human pilots, not requiring test-pilot skill levels or superhuman reflexes. Even limit speeds and loads are set with a safety margin in part because everyone screws up once in a while, even when trying to operate the aircraft correctly and within limits. That such safety margins exist doesn't mean that planning to exceed specified limits is a good idea.
Being allowed to solo during training doesn't mean being allowed to fly on your own accord. You'll still need to coordinate with your instructor, and if where you're learning to fly is anything like what it's like for me, the instructor will be watching and be just a radio call away while you're solo, just in case something goes wrong. Even longer-distance flying ("cross-country") solo before you have your license will require coordinating with your instructor, and you will almost certainly be limited in which airports you are allowed to fly to, precisely because the instructor needs to be certain that you can handle the conditions there. See Part-FCL.020(a).
Limits are set the way they are for a reason. Respect them. Go ahead and discuss with your instructor the reasons why those limits are what they are if you want to, but go into, and out of, that discussion with the knowledge that if you exceed them, you might get away with it some of the time, but you won't get away with it every time, and if you don't get away with it, the results can very easily get really ugly. Best case, you'll find yourself doing something like a dozen go-arounds in a row because you can't stabilize the approach well enough and don't have a well-established alternate you can go to. At that point, and with the fuel gauge needle heading steadily toward the red, will you be able to hold back the get-there-itis? What will that do to your ability to attempt to land the aircraft safely?
Quite frankly, if this question is indicative of your attitude towards aviation safety, then please do yourself, and others, a favor and stop piloting. You are going to get into an incident, or an accident. It's not a theoretical "slightly increased risk"; it's a very real thing. The simple fact is that landing with even a moderate crosswind (even more so if it's gusty, as it often is) is precision maneuvering at highway speeds, in a flight regime where you have the least precision available and the least margin within which to recover from an error.

"precision maneuvering at highway speeds" is also near the minimum flying speed of the aircraft, precisely the regime in which you have the least precision available -- limited control authority, limited acceleration, limited margin above stall -- as you say, it's asking to become a statistic.

"You'll still need to coordinate with your instructor, and if where you're learning to fly is anything like what it's like for me, the instructor will be watching and be just a radio call away while you're solo, just in case something goes wrong."-- obviously where this person (original asker of question) is flying, an instructor sign-off for solo is considered a ticket for unlimited unsupervised flying--

@quietflyer "obviously where [OP] is flying, an instructor sign-off for solo is considered a ticket for unlimited unsupervised flying" Or, more likely, they don't know what being allowed to solo under training actually means.

(I'd rather think that they are ignorant than that they are deliberately trolling.)

After receiving copious amounts of admonition for considering the "real" cross wind capabilities of your aircraft, I would add, THIS HAS NOTHING TO DO WITH BEING ALLOWED TO SOLO!  ANYTHING NEAR THE LIMITS OF THE SAFE ENVELOPE OF YOUR AIRCRAFT SHOULD BE CHECKED WITH AN EXPERIENCED INSTRUCTOR !!!
However, just like stalls, why not test AT ALTITUDE!
The cross wind limit of an aircraft is based on its ability to safely hold a straight line while landing.
Lawyers have figured out more money can be made sueing richer companies.  People who write your POH know this and will tend to be conservative about published values.
DO NOT DO THIS ALONE!  Go up with an experienced pilot to a safe altitude on a windy day and try to hold a ground track at slower and slower speed until you get down to your approach and landing speed.
A crab-kick out technique will probably be the best way to go.  You will find it is harder and harder to hold the line the slower you go.  Be ready with throttle, as wind may drasticly affect your ground speed and time in pattern.  Try "landing" at 2000 feet AGL. BE AWARE a gust from the wrong direction could result in a fatal stall/spin near the ground and landing in winds is far more dangerous.
This is great info to have in your "tool kit", expanding your knowledge envelope.  Get that info at altitude with a good instructor! But respect the weather, one crash is one too many.

"The cross wind limit of an aircraft is based on its ability to safely hold a straight line while landing."-- we could add the phrase "while keeping the wheels aligned with the runway. So- what are you envisioning? At altitude, as you slow down, how do you know if you are staying on the desired ground track with +/-10' or so of precision that is required to stay anywhere near the centerline of  the runway? In other words, how do you know that you've succesfully eliminated the very small deviations in ground track that we call "drift",which are trying to run your plane off the edge of the rnwy?

I can see how watching a GPS track could give you some idea of the maximum crosswind component which still allows you to bring your aircraft's heading into alignment with the ground track or vice versa-- which is the definition of a crosswind landing with no "drift".  You wouldn't want to land with MORE than that much xwind component, but as to whether you can really fly with enough precision to have a good landing with that much component, may be another question.

Still, good suggestion to do some experimenting at altitude..

Still, good suggestion to do some experimenting at altitude.Seems to me this pertains more to x-controlled slip than kick-out-the-crab technique. A cross-controlled slip can be maintained indefinitely, allowing you to check that your GPS ground track really is aligned with the a/c heading. It seems less clear how to practice kick-out-the-crab at altitude--should be no problem to adjust heading slightly to hold any desired ground track as you decelerate w/ xwind while flying in a coordinated manner-- then near stall speed, try to kick nose into alignment with ground track and see what happens?

I am envisioning keeping wheels straight with runway.

And yes, a x controlled slip is what we wind up with, and a single wheel touchdown.

To answer your first comment, you can tell drift by holding for a longer period of time while following the ground track (could be a highway). Secondly, kicking out the crab and moving to x controlled can be done anytime.  I preferred to do it just before touchdown as rolling in the slip gently reduces vertical  lift and sets it down easy.  Everybody has their ways.  Just hoping ambitious new solo flyer knows to stay in school rather than to trial and (big) error.

All I‘d like to add is a Tomahawk was purposely developed to spin easily. Really know how to exit a spin before trying asymmetric stuff in a Tomahawk.

In my experience, usually when people talk about a "kick out the crab" technique they mean applying downwind rudder pressure to align the nose with the runway, WITHOUT adding upwind bank to cancel drift.  That has to happen right before touchdown, or else you'll accumulate "drift" (actually a rudder-commanded turn).  We can read in magazine articles about flight training etc, debates about the pros and cons of this technique.  Certainly if your "kick" is actually a transition to a fully stabilized cross-controlled maneuver, that can happen any time.

I think people will get confused if they are reading about "kicking out the crab" when the writer really means a transition to cross-controlled slip.

Agreed.  Usually a "crab" is coordinated, thrust vector is helping too unless at idle.  Basicly the "kick" is compensated with more aileron.  Kick away from wind, aileron into wind for cross controlled (hopefully good) landing.